<!DOCTYPE html >
<html>
<head>
<title></title>
<meta  content="text/html; charset=utf-8" />
<style type="text/css">
html{
	height:100%;
}
.main{
	background-color:bule;
	height:100%;
	position:relative;
}
.content1{
	background-color: white;
	width:100px;
	height:100px;
	position:absolute;
	left:50%;
	top:50%;
	margin-left:-50px;
	margin-top:-50px;
}
</style>
</head>
<body>
 <div class="main">
   <div class="content1">
   </div>
 </div>
</body>
</html>